HIV often changes it shape due to the presence of an enzyme called reverse transcriptase. Reverse transcriptase, also known as RNA-directed DNA polymerase, an enzyme encoded from the genetic material of retroviruses that catalyzes the transcription of retprovirus RNA (ribonucleic acid) into DNA (deoxyribonucleic acid). This catalyzed transcription is the reverse process of normal cellular transcription of DNA into RNA, hence the name reverse transcriptase and retrovirus. Reverse transcriptase is central to the infectious nature of retroviruses, several of which cause disease in humans, including Human Immunodeficiency Virus (HIV).